The present invention pertains to the mining of coal and particularly to the use of longwall shearers in mining operations. Longwall shearers refers to continuous miners in which two rotating drums, referred to as the head drum and the tail drum, are used to shear the coal from a coal face that extends laterally from an access gallery in an underground mine. The shearer moves along the coal face cutting the coal from the face in one direction and then returns in the opposite direction when it completes cutting the coal from the face. As the shearer advances temporary roof supports or shields are moved forward to support the roof in the area where the coal has been removed. The section of the mine behind the temporary supports is allowed to collapse.
As can be readily appreciated, the operation of longwall shearers produces a large quantity of dust that must be contained in order for operators to function in the vicinity of the shearer. The dust is partially contained by an air flow which flows from the gallery into the lateral opening along the coal face. This air flow tends to circulate and force the dust toward the end of the lateral area, but in so doing, causes the dust to flow around the operators who are positioned on the shearer between the two rotating drums. Present Federal standards set a dust limit of 2 milligrams per cubic meter for mine operations and very few high production longwall shearers meet this Federal standard.
The prior art as described in an article entitled "Reducing Dust at Longwall Shearers by Confining the Dust Cloud to the Face" by Kissell et al, Tech Progress Report 111, Feb. 1981, of the Bureau of Mines Respiratory Dust Control Program, rely upon the use of passive barriers and water sprays to contain the dust. This article specifically describes dividing the air flow around the shearer into a clean air flow and a contaminant air flow by means of a passive barrier. The contaminant air flow is used to confine the dust cloud to the vicinity of the coal face while the shearer operators remain in the clean air flow on the opposite side of the machine. The air flow is improved by the use of water sprays that move the air like a small fan and can be positioned to direct the dusty air toward the coal face. A similar system is described in Report of Investigations 9037, Bureau of Mines, entitled "Using Barriers to Reduce Dust Exposure of Longwall Face Workers" by Robert A Jankowski and Charles A Babbitt. This report also describes the use of passive barriers for directing the air flow past the shearer in two streams; one stream being the clean air flow which is directed toward the shearer operators, the other air flow being directed to contain the dust cloud to the coal face. The report also refers to the above-referenced article for the suggestion that water sprays increase the effectiveness of the air flow in confining the dust cloud to the coal face. Similar descriptions of passive barriers are described in Technology News Releases, from the Bureau of Mines, US Department of the Interior, No. 116, Nov. 1981, "Modified Cutting Sequence Reduces Longwall Shearer Operators, Dust Exposure"; No. 119, Nov. 1981, "Reduce Dust on Longwall Faces with a Gob Curtain"; No. 121, Dec. 1981, "Spring-Mounted Screens on Shearer Reduce Operators, Dust Exposure"; No. 137, Mar. 1982, "Ventilation Curtain Reduces Dust from Cutting into Longwall Entry" and No. 205, Aug. 1984, "Reducing Longwall Face Workers, Respirable Dust Exposure from Roof Support Movement". All of these releases describe the use of passive barriers for directing the air flow in an attempt to confine the dust to the coal face. The reports also describe the use of water sprays to increase the effectiveness of the air flow in confining the dust cloud to the coal face. The water sprays all use conventional pressure spray nozzles that utilize pressurized water to produce the spray.
All of the above systems rely on passive barriers, either with or without the use of water sprays in an attempt to confine the dust cloud to the coal face. From the data described in the reports, none of these systems are effective in maintaining the dust level in a longwall shearer operation below the 2 milligram per cubic meter level set by the Bureau of Mines. The systems also require a large quantity of water when water sprays are used which presents the problem of supplying the water to the mine as well as disposing of the water in the mine.